Friday, November 04, 2016

Sputnik Planitia may Dominate Pluto




Pluto’s icy heart beats with a planetary rhythm.

When NASA’s New Horizons spacecraft whizzed by the dwarf planet in July 2015, it famously spotted a heart-shaped feature just north of the equator. Now, researchers are recognizing how that enormous ice cap drives much of Pluto’s activity, from its frosty surface to its hazy atmosphere.

Planetary scientists revealed their latest insights this week at a joint meeting of the American Astronomical Society’s Division for Planetary Sciences and the European Planetary Science Congress in Pasadena, California. Many of those discoveries revolve around Sputnik Planitia, the icy expanse that makes up the left lobe of Pluto’s ‘heart’. “All roads lead to Sputnik,” says William McKinnon, a planetary scientist at Washington University in St. Louis, Missouri.

Researchers already knew that Sputnik Planitia (formerly dubbed Sputnik Planum) is made mostly of nitrogen ice, churning and flowing in massive glaciers1. But its sheer size — 1,000 kilometres across and at least several kilometres deep — means that it exerts extraordinary influence over the dwarf planet’s behaviour.

The heart may have even knocked Pluto on its side. At the meeting, James Tuttle Keane of the University of Arizona in Tucson showed how the feature’s formation could have altered Pluto’s tilt. Sputnik Planitia may be a crater punched by a giant meteorite impact, which later filled with ice. The sheer mass of all that ice caused the dwarf planet to rotate relative to its spin axis, Keane says, so that Sputnik Planitia ended up permanently facing away from Pluto’s biggest moon, Charon. “Pluto followed its heart,” he says. (Other scientists, such as Douglas Hamilton of the University of Maryland in College Park, have suggested that Sputnik Planitia might have accumulated ice without an impact, and that the hole instead comes from the sheer weight of the ice depressing the ground beneath it.)

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